The present invention is directed to a device for facilitating tracking of an elastomeric belt used with a magnetic roll separator. More particularly, the present invention is directed to at least one thin strip of ferromagnetic or easily magnetizable material incorporated into an edge portion of the belt used in a magnetic roll separator, the magnetic field formed by the separator roll causing tracking of the belt.
Magnetic roll separators are used to remove ferromagnetic metals or para-magnetic materials from non-metals or from weakly magnetic material a) so that the commercially valuable fraction (usually the more strongly magnetic material) can be processed or, b) so that one fraction does not enter a machine or a process where such material could do damage to the machine or to the product being processed. Magnetic roll separators typically employ an elastomeric belt wrapped around two rollers, one of which, generally the head roller, is comprised of stacks of magnetic disks of rare-earth metals interposed with disk-shaped pole pieces. In use, material containing one or more magnetic components is dropped on the belt and the belt used to impel the non-magnetic material into a first collection bin on a trajectory determined only by the inertia of the material while the magnetic roller retains the more magnetic material in contact with the belt as long as the belt is in contact with the roller and drops it in a second bin, its trajectory being determined by the combination of its inertia and the force exerted by the magnetic field.
These belts pose a significant tracking problem for a number of reasons. First, the belts are very thin, typically between 2 and 20 mils, the thinner the better so as not to unduly abate the strength of the magnetic field operating on the material to be separated. Such paper thin belts can be easily shifted. An unbalanced load of material dropped onto the belt all too readily destabilizes the belt. Second, these belts have a very small length to width ratio. Such short, wide belts are difficult to guide. To further exacerbate the problem with the belts used in magnetic separators, the combination of thin belts and abrasive material results in rapid wear requiring frequent belt replacement. If the belt cannot be easily installed, tensioned, and stabilized, the system will have a large amount of costly down time. Further, belts that lose tracking easily are changed out more frequently since loss of tracking can result in damage to these thin belts. A belt which would track better would have extended wear life and require less frequent inspection to assure proper operation which, in turn, lowers manpower costs.
Traditional means of belt tracking are generally inappropriate in this application. Some belt trackers employ crowned pulleys or other means to shape the belt. In this application, it is essential that the head roller be as flat as possible in order to maximize the lateral distribution of the sortable material. Another technique involving mechanical engagement between the conveyor belt and the tracking roller, such as ribs on one and grooves on the other, produces accelerated wear in these thin belts, is generally not effective with short, wide belts, and the grooves are subject to filling by dust resulting in reduced effectiveness of the tracking technique and undesirable flexing of the belt adversely affecting load distribution. A third technique employs annular collars formed on the rollers to guide the belt back on track. These collars can be effective with thicker belts but in this application, produce accelerated wear of the edges and necessitate additional clearance around the pulleys which interferes with the separation operation.
The present invention overcomes these and other difficulties with traditional tracking systems. A thin strip of soft, magnetically susceptible material is incorporated in at least one of the belt edge portions. This soft magnetizable strip is subjected to the magnetic field created by the separator roller, the magnetic field having significant strength adjacent the outermost pole pieces, resulting in improved tracking of the belt. Any uneven loading causing a mechanical upset of the belt will quickly be overcome and the belt stabilized as a result of the magnetic attraction between the magnetically susceptible strip and the magnetic field created by the separator roller. This provides a persistent self-centering force which makes the belt easy to install, requires minimum head/tail roller adjustment, and provides extended belt life since there is no mechanical engagement with the belt which could produce accelerated wear. The strip of magnetically susceptible material can take any of a number of configurations and may be attached in any of a number of different manners. The ferrous material may be encased in a urethane elastomer, for example, the urethane sandwiching the edge of the belt. Alternatively, the urethane may partially encase the magnetizable material and be directly attached to the upper or lower face of the belt adjacent one or both edges. The magnetizable material may take the form of a cable and have the edge of the belt wrapped there around and secured by adhesive, or the like. Alternatively, the magnetizable material may take the form of a woven wire mesh which is incorporated into the edge portion of the belt.
Various other features, advantages and characteristics of the present invention will become apparent to one of ordinary skill in the art after a reading of the following specification.